It is known to stretch a fiber-fleece slubbing strip in a stretching arrangement comprising a plurality of roller pairs which engage the strip of the fiber-fleece slubbing within the nip of each roller pair. Two such slubbings can be provided, each being twisted together with a core thread and the composites (each of a slubbing strip and core thread) being twisted together in a ring spindle, flyer spindle or like spinning or twisting arrangement.
The resulting core yarn thus has at least two core threads disposed generally within a body of the fiber-fleece material which originally formed the slubbings. A fiber-fleece slubbing comprises, according to the invention and the prior art, a strip of intertwined but nonwoven fibers which are held together by mutual frictional contact. The core yarn can be a continuous monofilament or a thread made from a plurality of monofilaments. An advantage of a core yarn fabricated in the manner described is that it can have an external characteristic similar to that of the natural fiber from which the slubbing is constituted while possessing a strength equal to or greater than that of the monofilaments forming the core threads.
A process in which a core yarn is formed in the manner described above is known from Swiss Pat. No. 395,819 (U.S. Pat. No. 3,264,816). In this prior art process, the rollers of the last pair as well as the rollers upstream therefrom have large lengths (cf. page 2, right hand column, lines 98 and 99) to permit the fiber-fleece strips or slubbings to be separated from one another by large distances. A respective core thread is then led to each of the strips at the last roller pair of the stretching device. Each strip and the associated thread are then twisted together. Later, the combinations, each of a strip and core thread, together are passed through a thread guide in an axial extension of a ring spindle to twist them together. Hence the vertex of the twisting triangle lies at this thread guide.
While the conventional process gives a high resistance to sliding movement of the fiber-fleece material along the core threads, it has been found that this sliding resistance stability against relative longitudinal shifting of the fiber-fleece strip and the core thread is not fully satisfactory.